Date: Thu, 11 Nov 2021 07:45:51 +0000
From: HAGIO KAZUHITO(?????)     <k-hagio-ab@nec.com>
To: Philipp Rudo <prudo@redhat.com>
Cc: "Discussion list for crash utility usage,   maintenance and
        development" <crash-utility@redhat.com>
Subject: Re: [Crash-utility] [PATCH] Fix live debugging with
        lockdown=integrity
Message-ID:
        <TYYPR01MB67772F7C8616E337FF66787CDD949@TYYPR01MB6777.jpnprd01.prod.outlook.com>

Content-Type: text/plain; charset="iso-2022-jp"

-----Original Message-----
> With kernel lockdown the access to kernel interfaces that allow to
> extract confidential information (lockdown=confidentiality) or modify a
> running kernel (lockdown=integrity) can be restricted. Two of the
> interfaces that can be restricted are /dev/mem (integrity &
> confidentiality) and /proc/kcore (confidentiality). With
> lockdown=integrity this leads to a situation where /dev/mem exists but
> is not readable while /proc/kcore exists and is readable. This breaks
> crash's live debugging when it is invoked without argument, i.e.
>
> $ crash
> [...]
> crash: /dev/mem: Operation not permitted
>
> while passing /proc/kcore as image succeeds. The reason for this is that
> crash always picks /dev/mem as source when it exits but doesn't check if
> it is readable. Fix this by only selecting /dev/mem when it is readable.
>
> Signed-off-by: Philipp Rudo <prudo@redhat.com>

Thank you for the patch.

Acked-by: Kazuhito Hagio <k-hagio-ab@nec.com>

Kazu

> ---
>  filesys.c | 2 +-
>  main.c    | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/filesys.c b/filesys.c
> index 3361b6c..43cbe82 100644
> --- a/filesys.c
> +++ b/filesys.c
> @@ -3666,7 +3666,7 @@ get_live_memory_source(void)
>       if (pc->live_memsrc)
>               goto live_report;
>
> -     if (file_exists("/dev/mem", NULL))
> +     if (file_readable("/dev/mem"))
>               pc->live_memsrc = "/dev/mem";
>       else if (file_exists("/proc/kcore", NULL)) {
>               pc->flags &= ~DEVMEM;
> diff --git a/main.c b/main.c
> index 71c59d2..b278c22 100644
> --- a/main.c
> +++ b/main.c
> @@ -1119,7 +1119,7 @@ setup_environment(int argc, char **argv)
>       pc->flags2 |= REDZONE;
>       pc->confd = -2;
>       pc->machine_type = MACHINE_TYPE;
> -     if (file_exists("/dev/mem", NULL)) {     /* defaults until argv[] is parsed */
> +     if (file_readable("/dev/mem")) {     /* defaults until argv[] is parsed */
>               pc->readmem = read_dev_mem;
>               pc->writemem = write_dev_mem;
>       } else if (file_exists("/proc/kcore", NULL)) {
> --
> 2.31.1